---
 include/linux/skbuff.h | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index e6bfe5d0c525..30a8dc4233ba 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h

@@ -671,7 +671,13 @@ enum {
 	/* This indicates the skb is from an untrusted source. */
 	SKB_GSO_DODGY = 1 << 1,
 
-	/* This indicates the tcp segment has CWR set. */
+	/* For Tx, this indicates the first TCP segment has CWR set, and any
+	 * subsequent segment in the same skb has CWR cleared. However, because
+	 * the connection to which the segment belongs is not tracked to use
+	 * RFC3168 or AccECN (RFC9768), and using RFC3168 ECN offload may clear
+	 * ACE signal (CWR is one of it). Therefore, this cannot be used on Rx.
+	 * Instead, SKB_GSO_TCP_ACCECN shall be used to avoid CWR corruption.
+	 */
 	SKB_GSO_TCP_ECN = 1 << 2,
 
 	__SKB_GSO_TCP_FIXEDID = 1 << 3,

@@ -706,6 +712,14 @@ enum {
 
 	SKB_GSO_FRAGLIST = 1 << 18,
 
+	/* For TX, this indicates the TCP segment uses the CWR flag as part of
+	 * ACE signal, and the CWR flag is not modified in the skb. For RX, any
+	 * CWR flagged segment must use SKB_GSO_TCP_ACCECN to ensure CWR flag
+	 * is not cleared by any RFC3168 ECN offload, and thus keeping ACE
+	 * signal of AccECN segments. This is particularly used for Rx of
+	 * virtio_net driver in order to tell latter GSO Tx in a forwarding
+	 * scenario that it is NOT ok to clean CWR flag from the 2nd segment.
+	 */
 	SKB_GSO_TCP_ACCECN = 1 << 19,
 
 	/* These indirectly map onto the same netdev feature.

-- 
2.34.1